Television system and method



July 5, 193s; L, DE FOREST 2,122,456

TELEVISION SYSTEM AND METHOD' Filed lom. s, 193sv 4 sheets-sheet 1INVENTOR. Lee de Fares ATTORNEYS July 5, 1938. DE FOREST TELEVISIONSYSTEM AND METHOD Filed oct. 5, 193e 4 sheets-sheet 2 1NVENTOR.

Lee de Fores ATTORNEYS July 5, 1938. L. DE FOREST TELEVISION SYSTEM ANDMETHOD Filed Oct. 3, 1936 4 Sheets-Sheet 3 INVENTOR.` l. ee de ForesATTORNEYS July5,193s. L DE FOREST 2,122,456

TELEVISION SYSTEM AND METHOD Filed Oct. 5, 1936 4 Sheets-Sheet 4INVENTOR. L e de Fares af ATTORNEYS Patented July 5, 1938 UNITED STATESPATENT OFFICE TELEVISION SYSTEM ANDl METHOD Application October 3,

11 Claims.

An object of the invention is to provide apparatus for radial scanningin a television system. Another object of the invention is to provide aradial scanning system for television in which .51 there are novibrating parts.

Another object of the invention is to provide a novel television scannerconsisting of a disc or drum having a zig-zag linear aperture, andapparatus for and method of operating the same.

Another object of the invention is to provide a radial scanning systemin which the picture may be of any desired shape without the necessityof using biasing voltages in order to produce this result.

Another object of the invention is to provide a scanning system havingan intricate interweaved scanning pattern.

Another object of the invention is to provi-de a radial scanning systemwhich avoids irregularities in the degree of illumination at the centeror at the borders of the picture.

Another object of the invention is to provide an apparatus and methodfor linear scanning with a scanning disc or drum having a zig-zag linearaperture.

Other objects of the invention will be apparent from the drawings andthe following description of the features of the invention and in theprovision of apparatus and methods of operation for accomplishing theforegoing objects.

In the drawings,

Fig. 1 is an elevation partly in section of a portion of one species ofmy invention in which my novel scanning disc is used;

Fig. 2 is a section along the lines of 2-2 of Fig. 1;

Fig. 3 is an enlarged schematic View illustrating the cooperationbetween a plate having a linear aperture which I use in connection withmy scanner, and the zig-zag linear aperture of the scanner itself;

Fig. 4 is an elevation of another form of my invention in which ascanning drum is used;

Fig. 5 is a section along the lines 5--5 of Fig. 4;

Fig. 6 is a schematic showing oi another species of my invention inwhich my novel scanning disc is used;

Fig. 7 is a, front elevation of my viewing screen 50 with a portion ofradial scanning lines outlined thereon;

Fig. 8 is an enlarged schematic showing illustrating the operation of myZig-Zag linear aperture in the scanning disc and drum, and furtherillustrating the arrangement of this aperture to 1936, Serial No.103,844

secure a picture that may be square or of any other -desired shape;

Fig. 9 is a view illustrating the nature of the scanning patternproduced with my novel scanning arrangement;

Fig. 10 is a view of a modification of an aperture in an opaque plate inorder to produce a desired amount of illumination;

Fig. 11 is a side elevation partly in section, illustrating how my novelscanning means may be used to produce parallel line scanning;

Fig. 12 is a schematic view illustrating a portion of the apparatusshown in Fig. 11;

Fig. 13 is a diagrammatic view illustrating the parallel line scanningobtained with the Figs. of 11 and l2, or Fig. 14; and

Fig. 14 is a partial elevation of a modification of the apparatus shownin Figs. 11 an-d 12 in which parallel line scanning is obtained with mynovel scanning disc.

In my application Serial No. 70,061, iiled March 21, 1936, for Radialscanning television system I have disclosed a television scanning systemin which a vibrating mirror is mounted upon a resonant torsional'memberand located in line with axis of a small motor, and is caused to rotateby said motor at the same time that it is vibrating or twisting througha plane at right angles to the axis of the motor. By this arrangement abeam of light reflected from the vibrating and rotating mirror is causedto trace a multiplicity of approximately radial lines of light upon ascreen, the center of which is located in line with the axis of themotor.

The invention herein described attains the same general object of radialscanning without any vibrating mechanism, and may also be used to obtainrectangular, linear scanning. By means of the present invention I amenabled not only to avoid any complications which might occur due tochanges in the mechanical vibrating system, etc., but I am enabled touse much larger mirror surfaces with resulting enhanced intensity oflight upon the viewing screen. I am also able to throw upon the screen apicture of any desired shape such as square, oblong, oval, etc., withoutthe necessity of using biasing voltages as disclosed in my copendingapplication above referred to.

Similar reference numerals refer to similar parts throughout thespecification.

In Figs. 1 and 2 a circular opaque disc l is mounted with its center inline with the shaft of a synchronous motor 1. The disc l has arrangednear its periphery a series of transparent zigzag lines 3 of equalspacing and length arranged in circular formation. These transparentlines may be made by sawing or cutting zig-Zag lines in a metallic disc,or the disc may be a glass photographic plate and an enlarged black andwhite drawing of the desired dimensions may be photographed thereon,preferably with photographic `reduction of dimensions in order to reduceany 'errors or irregularities which may exist in the original drawings.In one form of the invention which I have constructed, this circularphotographic plate I is 6 inches in diameter and` carries a central,circular orice 2, one-half inch in diameter. The length of theindividual lines of the circular zig-Zag pattern is one-half inch. Thisopaque plate is preferably mounted in a vertical plane with its center ashort distance from the end of the projecting shaft 6 of the motor ll.It may be mounted in a pheripheral rim 5E:- of metal or plastic in orderto support it. The shaft 6 of the motor 1 carries a radial arm I 5attached tothe outer end of which is a thin, opaque plate 4 whichcarries a radial slit 5 so arranged that the plate 4 travels in acircular path close to, and parallel with the opaque disc I. The radialarm I5 also carries an incandescent lamp 8 having a filament so arrangedthat it represents a continuation of the radial line of the arm I5, andis therefore parallel to the slit 5 in the plate or the new highpressure capillary quartz mercury vapor lamp may be used. A smallsemi-cylindrical condensing lens 9 may be placed between the lightsource 8 andthe plate 4, so arranged so that the light of the filamentis concentrated upon the slit 5, and a cylindrical reflector I0 may bemounted behind the lamp to increase the brilliancy of the light. Onelead from the lamp 8 may be connected through a conductor IE to aconnector ring I2 mounted upon the shaft the motor. Bearing on thisconnector ring is a brush I3 which is connected to a suitable source ofpotential I4 to light the filament of the lamp. The return lightingcircuit is completed to the arm I5 and the frame of the motor T. Themotor should preferably be a single phase synchronous motor of i800 or3600 revolutions per minute.

By the above described arrangement I obtain through the disc I, a smallpoint of light 3i, Fig. 3, through the small diamond shape apertureformed where the radial slit intersects or crosses one of the Zig-Zagtransparent lines in the opaque disc I. The point of light thus obtainedmoves in and out along the radial line towards and from the center ofthe circular disc I as the lamp 8 and the plate 4 carries in a circularmotion around and close to the transparent zig-Zag track the opaque discI.

In connection with the apparatus shown in Figs. 1 and 2 I employadditional apparatus as shown in Fig. 6 and described in connectiontherewith. I also may employ a system of gears and connections BU, 6I,62, 53, 64to move the disc I in order to vary the scanning pattern. Thiswill be described later. For the purpose of the description up to thispoint the disc I may be considered as stationary.

Instead of the opaque discy carrying the Zigzag transparent line asdescribed above in connection with Figs. 1 and 2, I may employ for myscanner an opaque cylindrical strip I1 as illustrated in Fig. 4 throughthe surface of which a transparent Zigzag line I8 has been cut, or ifthe strip' be of glass has been photographed as above described. In Fig.4 the synchronous motor 'I constitutes the driving means as before andhas fixed to an armI 5 a reflector III, linear light source 8, lens 9,and opaque plate 4' having a linear slit 5. The opaque cylindrical bandI'I is stationary and its center lies in the axis of the shaft of themotor 1. The intersection or crossing of the slit 5 with the zig-Zagslit I8 in the periphery of the cylindrical band Il results in a diamondshaped point 3|, Figure 3, as before, through which a small pencil oflight is projected radially toward the axis of the motor. As the motordrives the lamp 8 and plate 4 around the periphery of the band I'I andin close proximity thereto, this point of light travels back and forthto and from a plane perpendicular to the axis of the motor and. in thedirections always parallel to said axis. Also secured to the shaft ll ofthe motor 'I and rotated thereby is a funnel shaped holder 35, withinwhich, and rotated therewith, are mounted a mirror 34 at an angle of 45degrees with the plane of the cylindrical band I1, a Kerr cell having acircular polarizing plate 52, a circular analyzing polaroid plate 5i,and a condenser system 53, 54. A cross section of the Kerr cell takenalong the line 5=5 of Figure 4 is shown in Figure 5 with the samereference numerals.

A brush 51 bearing upon the periphery 55 of an 'i insulated collectorring mounted on the holder 35 is electrically connected to one outputterminal of the modulating amplier which suppliesk the televisionsignals, while the other terminal of said modulator is connected to theframework of the apparatus.

Also mounted within the holder 35 and rotating therewith is a lens 31which may be a spherical lens, or a cylindrical lens with its axis setat right angles to the axis of the cylindrical lensr 9 in order to focusthe beam of light after is reiected from the mirror 34 so that at thescreen 38 it becomes a small point of light. If the mirror 34 were aplane mirror, as indicated in broken lines, the beam of light from theaperture which is shifting in planes radial to the shaft of the motorand towards or from a plane perpendicular to the axis of the motor,would be caused to lill a cylinder of light as the motor and lightsystem rotate. Such cylinder of light is indicated by the broken lines32 in Fig. 4. If, however, in place of the iiat mirror I employ a convexcylindrical mirror 34, the shifting beam of reflected light is caused tospread out radially so that the limits of its trajectory represent aconical instead of a cylindrical envelope, as indicated by the fulllines from the mirror 34'v to the points nearer the upper and loweredges of the viewing screen 38. The angle of this cone may be madeanything desired within reasonable limits simply by increasing the angleof curvature of the convex mirror 34. A slit 35 in the side of theholder 35 admits light from the lamp 'Sto the mirror 34.

The area of the beam of light upon the viewing screen depends upon thesize of the picture area but ordinarily I prefer to restrict it'to anarea equivalent to that of a circle -fg to 1A; inch diameter, when thescreen is of Ithe order of '34 inches in diameter, if a circle, o1' 24inches on each side if a square. The screen 38 is preferably located 4or 5 feet from the mirror 34 and may of course be of translucentmaterial and viewed from behind.

In Fig. 6 I have illustrated diagrammatically an arrangement whereby thelight source instead of being attached to the motor shaft and made totravel in a circular path may be stationary. In this figure I have againshown a reflector IIJ and a linear light source 8, and a condensing lens55.- I have shown the-Kerr'cell 5 I-54;which kning lines A--A outlinedthereon.

laisance receives .themodulated signal wave, in line with the beam oflight from the lamp 8. A synchronous motor 'l is again used. In thiscase it is provided with a hollow shaft, which is preferably blackened,and the light system is mounted axially with respect thereto so as todirect the beam through the shaft. Mounted on an arm secured to themotor shaft is a 45 degree mirror or prism 22, a second45 degree mirror23, a lens 9, and a plate 4 with a slit 5. Mounted on another armsecuredto the motor shaft is another 45 degree mirror 24 and another 45degree convex mirror 25. The stationary scanning disc l, which is againan opaque disc with zig-zag transparent circular lines as alreadydescribed in Figs. 1 and 2, is placed between the two mirrors 23 and 24.The light from the lamp 8 after being modulated in the `Kerr cell isreflected from the mirror 22 tothe mirror 23 where it is condensed intoa narrow vbeam of light by the lens 9 and projected through the slit andthe zig-zag aperture 3. Itis then reflected by the mirrors 24 and 25 andfrom there, due to the rotation of the light vand mirror system,projects as a cone of light through the mask 40 and lens 26 onto thescreen 38. A slit in vthe hollow shaft 6 of `the motor 'l permitsV thenarrow beam of light to be reected from the mirror 22 to the mirror 23.The axially shifting pencil of light which is reflected from the mirror`24 upon the mirror 25 is there reflected so that it describesapproximately radial lines upon the` screen 38, completely covering thesame in the form of a circular area of illumination as in the case ofthe apparatus shown in Fig. 4. The mirrors 24 and 25 which are carriedon an arm rotated by the motor shaft, and the lens 26 and mask 40 mayalso be used in connection with the apparatus shown in Figs. 1 and 2 to`complete the system there described. It will thus be seen that in thecase of the apparatus .caused toscan the entire surface of the viewing'screen so that the signals will be reproduced.

Ihe lens 26v of Fig. 6l may be made spherical and remain stationaryinstead of being cylindrical and rotating with the motor shaft, as inthe case of the lens 31 of Fig. 4. A similar sta- .tionary lens could,of course, also be used with Fig. 4.

I In Fig. 7 I have shown the viewing screen in front elevation with aportion of the radial scan- If it is desired to show only a square framepicture, such as outlined in broken lines D, E, F, G, I may employ amask of non-reiiecting material, such as blackl velvet, to mask theviewing screen, or I mayv employ a square metal mask, such as 4U in Fig.6, located between the revolving convex mirror 25 and the stationarylens 26; or if the lens 26 is attached to the frame 35 as the lens 3l inFig. 4, and made to rotate with the mirror 34, this stationary frameshould be placed between `the-lens 3T and the screen 38. The area ofillumination will then be cut down to the shape of a square, asindicated by the broken lines D, E, F,- G, and the scanning lines B-B,Fig. 7.

Inasrnuch as all of the radial paths traversed by the light beam mustpass through the center of thel screen as at C, Fig. 7, this portion ofthe screen becomes more luminous than the outlying sections,notwithstanding the fact that the light beam traverses the centersectionwith the maximum velocity of transit. Similarly, around the peripheralsection of the circular screen illumina.-

tion where the radial movement of the light beam is slowed up andreversed in direction, there exists a brighter ring of illumination. Ifthe mask D, E, F, G, is not used and the picture therefore vis circularin outline, this latter ring affords an artistic circular framebordering the projected television picture. If the square masking frameD, E, F, G is employed, this bright peripheral ring is masked from Viewexcept for a small portion in each of the four corners of the picture.

It is usually desirable that the central area of the screen be no morebrightly illuminated than the remaining portions. To accomplish this, Isimply darken a small circular area of the screen as shown at C', Fig.7, preferably by lightly spraying it with some opaque, or poorlytranslucent, or poorly reflecting material.

When the above described square mask is employed, the four arcualsections of the illuminated circle are lost to View, the sweeps of thepoint of light which extend beyond this square frame being quiteuseless. However, by altering the lengths of successive lines of thezig-zag aperture in my scanner it is possible to limit the excursions ofthe beam so that the envelope of the reversal points will become asquare in outline. Such an arrangement is illustrated in the circulardrum scanner of Fig. 4 and in enlarged detail in Fig. 8.

Referring to Fig. 8, I have there shown an enlarged plan view of thecircular drum l1 with the zig-zag aperture IB so arranged that the twosymmetrical envelopes upon which the successive apices of the zig-zaglines around the cylindrical drum terminate, instead of being parallellines, follow a secantial form. In this iigure the divisions along thehorizontal or abscissal axis represent equal angular deflections of theradial beam about the central axis of the motor shaft. 'I'he ordinatesof the two symmetrical curves are proportional to the successive secantsof these angles from zero to 45 degrees, from which limiting angle thecourse of the envelope or secantial curve is reversed, inasmuch as theradial deection at the 45 degree angle of the horizontal line is themaximum actually obtained. If, therefore, the lengths of the zig-Zagtransparent lines photographed upon or cut through the circular band Ilof Figs. 4

and 8 are limited in accordance with this secantial quadrant curve, fourtimes repeated about the circumference, I obtain corresponding increasesand decreases of the radial excursions of the beam of light reflectedfrom the convex mirror 34 as the optical system is rotated, and therebyobtain a square picture. Similarly, where I employ a circular opaquedisc I as in Figs. 1, 2 and 6, I may also limit the radial sweeps of thebeam of light so that its limiting envelope upon the viewing screenbecomes a square instead of a circle.

The envelope limiting the zig-zag transparent lines as these extendaround the band Il or the disc I may be arranged in any desiredarbitrary manner so that I may throw upon the viewing screen a pictureof any desired shape or form, for example, rectangular, oval,elliptical, etc.

In Fig. 8 the opaque shield 4 is indicatedin broken lines with the lightslit 5 therein. The transparent lines in the opaque drum or disc insteadof being straight may be made slightly curved if desired in such amanner as to equal ze to some extent the speed of transit of the lightspot over the surface of the viewing screen. Also the bright spot ateach terminus of the radial excursion of the beam over the surface ofthescreen may be obliterated by simply separating the ends of each pair ofconverging zigzag lines at their terminae upon an opaque disc or drum sothat when the straight line slit in the moving member 4 passes acrossthe apex of two approaching zig-Zag lines nolight is transmittedtherethrough.

Similarly, instead of rendering more opaque or less reflective a smallcentral area of the viewing screen, I can make the central region of theZig-zag lines narrower than the outer portions thereof so that'lesslight is transmitted at the point where the slit crosses the centralportion of each zig-zag line, thereby automatically reducing thebrilliance of the central region of the viewing screen. Or, asillustrated in Fig. 10, I may make the slit 5 narrower at its centralregion than it is at its extremities in order to accomplish this sameresult.

I have pointed out that the speed of transit of the light spot as itcrosses the central area of the viewing screen is at a maximum and alsothat all diametric excursions of the light are concentrated in thiscentral area. This constitutes one of the especial advantages of myradial type of scanning as the central portions of any picture areusually the most important portions and demand the greatest amount ofillumination and the maximum neness of detail. These qualities areautomatically afforded by the increased speed of the spot over thecentral section of the picture and by the fact that the spot of lighttraverses these central sections twice for every diametric excursion ofthe spot regardless of the peripheral separations of the radialexcursions. v

`In Fig. 9 I have outlined the approximate paths which the radiallymoving spot of light actually traverses over the surface of the screen.Therein the line 0 1 represents the first radius over which the beam oflight would be deflected outwardly from the center of the screen if saiddeflection were at infinite speed. As'the speed is not infinite the spotinstead follows the narrow elliptical or approximately elliptical pathas there shown between the radiallines 1 and 2. Thus the return of thespot of light approaches the straight radial line 2 as the spotapproaches the center of the circle and its speed of travel iscorrespondingly increased. When the spot passes the center and goes intothe lower section of the circle its trajectory instead of lighting the,screen between the extensions of radii 1 and 2 will light it betweenthe extensions of radii 2 and 3 and upon the re-entry of the spot intothe upper sector of the circle it will traverse the space between radii.3 and 4, and so on around the circle until one-half of a revolution ofthe motor shaft has been completed. Thus if there are 64 diametricexcursions of the spot `of light during one revolution of the motor, thelast excursion of the spot of light before a half In order to obtain amore intricate interweaving of scanning lines across the face of thepicture than the simple alternate weaving above described, I may slowlyrotate (or oscillate through a small angle) the fixed opaque disc l ofFigs. 1, 2 and 6, or the drum I'l of Fig. 4, in a direction preferablyopposite to the direction of travel of the radial arm I5. This slowmotion of the disc or drum may be Very simply effected by meansillustrated in connection with the disc in Figures 1 and 2 in which Ishow a worm 60 on the motor shaft meshed with a gear 6| on a flexibleshaft 62 which terminates in a spur gear 63 meshing with gear teeth 64in the periphery of the frame which supports the disc l. In such anarrangement I may choose a speed reduction ratio between the number ofrevolutions of the motor shaft and that of the opaque disc or drum whichis incommensurable. When such a gear ratio or uneven speed ratio ischosen the motor must theoretically make a very great number or even aninfinite number of revolutions before any given path of the scanningspot across the screen exactly repeats itself. I thereby obtain theeffect of an extremely complicated system of line interweaving which hasnever been remotely approached by any other known method of scanning,either mechanical or with the cathode beam. It is thereby impossible forthe human eye to detect a marked linear action or linear quality of theprojected television picture. This adds greatly to the sense ofcontinuity of the picture thus projected as well as affording afinen'ess of detail which is quite impossible to obtain by any ordinarymethod of interweaved scanning.

In Figs. 11, 12 and 14 I have shown an arrangement whereby the essentialelements of Figs. l, 2, 4 and 6 are used but in which by maintaining thesource of light, the rectilinear slitvand the convex mirror stationarywhile the opaque disc or drum is rotated at high speed, I can obtain aparallel line scanning of the screen or object such as is had with themore conventional devices for scanning known in the art to-day.

In Fig. 11v I have illustrated apparatus for accomplishing this resultwith the opaque drum I1. In this case all of the transparent zig-zaglines I 8 are of the same length. I mount the drum upon the shaft of thesynchronous motor 1 and centrally locate it with respect lthereto andattach to the frame of the motor by an arm 'IT the linear source oflight 8, reflector IIJ, lens 9, and plate 4 with slit 5, with the linearlight source and aperture placed parallel to the axis of the motor shaftand so located that the cylindrical surface of the drum I1 passes underand close to the plate 4. Between the drum l1 and the motor shaft Imount the convex 45 degree mirror 34 in fixed position upon an arm T8 sothat its chordal plane is at right angles to a vertical plane passingthrough the axis of the motor shaft. The mirror 34 need not be locatedin line with the axis of the motor shaft but is preferably quite closeto the inner surface of the drum I1. This arrangement gives me a sweepup and down ina vertical plane of the beam or pencil of light whichpasses through the crossed apertured line of the drum and fixed plate asthe drum revolves. 'Ihe angle of deflection of this beam in the verticalplane may be made as large as desired with.

in reasonable limits by altering the convexity of the mirror 34. Inorder to scan completely a viewing screen or object by means of thisrapidly moving pencil of light, it is now necessary merely to cause thevertical plane of its sweep to move horizontally and to repeat thishorizontal movement periodically. This is simply accomplished by the useof a plane mirror or mirrors 80 rotating about a vertical axis whichmaybe driven by a gear 6| on the motor shaft which meshes with a gear 82on which the mirror is mounted in order to move the mirror insynchronism with the scanning drum Il. A four sided or polygonal drummirror 8i) may of course be used instead of a simple planedouble mirrorand by properly arranging the mirrors 34 and 8U relatively to each otherin a manner wellrknown in the art it is possible to obtain essentiallycontinual illumination of the screen.

In Figure 12 I have shown a diagrammatic plan view of the apparatus ofFigure 10 in which the opaque plate 4, slit 5, mirror 80, and screen 38are shown.

I have also illustrated in Figure 13 the scanning pattern from which itwill be seen that the object or viewing screen is scanned in parallelvertical lines.

With an arrangement for rectangular parallel line scanning such as Ihave described, I prefer to employ motor and mirror speeds for a givennumber of zig-zag lines about the apertured drum to give 200 to 300vertical sweeps of light per sweep of the horizontal deflecting mirrorand 24 or 30 such horizontal sweeps per second. The former defines theline frequency and the latter the so-called picture frequency ofscanning.

In Figure 14 I have disclosed an alternative arrangement for parallelline scanning in which a zig-zag apertured disc l similar to that shownin Figures 1, 2 and 6 is used. In this case, however, the reflector I0,linear light source 8, opaque plate ll with its light slit 5, and convexmirror 34 are stationary, while the disc I is being rotated by the motorl. I also rotate a mirror or mirror system 8U by means of gears 6| and82 similarly to Figure 11. In this case the beam of light is reflectedback and forth in a horizontal path across the screen 38 and itsvertical movement is controlled by mirrors 80. To obtain vertical linescanning which gives better picture effects than does horizontal, it isnecessary only to mount the apparatus so that the motor shaft isvertical rather than horizontal.

I have also shown in Figure 14 a Kerr cell 5l, 52 for producing amodulated beam in accordance with signal modulations, between the lightsource 8 and the opaque plate 4. The Kerr cell may be used in a similarlocation in the showing of Figure 11 or it may bev located as shown inFigure 4.

Regardless of how complicated the scanning pattern of the televisionreceiver may be, as for example with the apparatus illustrated in Figurel, it is only necessary that an identical scanning pattern be followedat the transmitter and that perfect synchronism between transmission andreceiver motors be maintained in order to receive successfully thepicture which is being transmitted. Therefore the descriptions ofvarious types of mechanism above in connection with a televisionreceiver will apply equally for pickup scanning devices, with thesubstitution, of course, of a `fixed brilliant spot light source at thetransmitter pickup in place of the modulating light which I havedescribed in conenction with the receiver scanning apparatus. Thus, forexample, if I am illuminating the object at the transmitter by means ofthe so-called flying spot, the arrangement of Figures 1, 2 and 11 isapplicable, or the arrangement shown in Figures 4, 6 and 14 may bedirectly substituted as the flying spot pick-up simply by omitting thelight modulating arrangement there shown. In other Words, the source oflight for the iiying spot pickup may be either stationary as shown inFigures 6, 11 and 14 or may be mounted on a radial arm driven by thesynchronous motor as shown in Figures 1, 2 and 4.

It is of course necessary that the synchronous motors at the transmitterand receiver stations be kept in exact synchronism. I have found thatwhen single phase synchronous motors of suiiicient power are employedperfectly satisfactory synchronism may be obtained by simply connectingthem to the same power network, even though there may be from time totime slight variations in the exact cycle speed of the powerhousegenerators supplying the mains. As both synchronous motorsare identicalany slight alteration in driving speed from the powerhouse will affectall such motors alike.

If, however, it is desired to synchronize a transmitter station with areceiver lying outside of the same lighting supply district, thereceiving motor may always be kept in perfect synchronism by means wellknown in the art, such as by transmitting a synchronizing signalintermingled with the television carrying signal, filtering thesynchronizing signal out from the picture signal at the receivingstation, amplifying this synchronizl ing signal, and causing it tocontrol b y means of a small so-called sonic motor a larger motor ofadequate power, which motor may be supplied from any suitable source ofcurrent.

The exact shape of the spot of light which I obtain from instant toinstant as the straight line slit 4 passes the zig-zag slit, while ingeneral of diamond shape as illustrated at 3|, Figure 3, may slightlyalter its shape while passing through the scanning cycle. This change ofshape of the spot is unimportant so long as the area of the spot ismaintained sufficiently small for satisfactory fneness of picture detailand so long as the spot upon the receiving screen is identical in shapeand location with the corresponding flying spot produced by thetransmitter pickup.

While I have mentioned a flying spot pickup at the transmitter, it isequally possible by means of my apparatus described above to scan asmall photograph, as when transmitting motion pictures from a positivefilm. In this case the lm is held stationary in front of the flying spotsignal and sufficiently close thereto so that a frame of the motionpicture film lies entirely within the circular area scanned by theflying spot or within the rectangular area scanned if the zig-zag linein the opaque section is of the type illustrated in Figures 4 and 8. Foriilrn scanning purposes the whole scanning device is made suflicientlysmall and the projected spot sufficiently fine that the necessary detailof the small picture is obtained. Additional lenses may of course beemployed, if necessary, in a manner well known in the art. The iiyingspot or pencil of light passes through the transparent film and fallsupon the cathode of a photoelectric cell having a sensitive surface ofarea equal to or larger than the projected motion picture frame.

By my system of scanning, it is obvious that the motion picture framebeing scanned should be held stationary for a period at least equal tothat of a complete scanning cycle, that is of one revolution of themotor. Inasmuch as the standard speed of motion picture projection is 24picture frames per second, it is desirable that my motor shall turnv ata speed of 24 or more revolutions per second. .11 For directpickup, as'of outdoor scenes or from a brilliantly illuminated stage, I prefer touse a large lensfas in a portrait camera and project the' picture of theoutside scene or stage scene upon the ground glass of such a camera,behind which I locate my pickup scanning mechanism. This screen ispreferably of lsmall dimensions to give maximum light intensity toii'theprojected scene. I then use a photoelectric cell in place of the ylamp8, the leads from which are carried tothe rst stagelof the photoelectricamplifier, using acollector Vring and brush as in Figure l for one leadand Ythe motor frame for the other the photoelectric cell is mounted forrevjplution as in Figures 1, Zand 4. Then in addition to or substitutionfor the cylindrical lens 37, Figure 4, I prefer to employ a narrowviewing slit-placed in front of said lens and parallel to its axis.'I'he thicknessof the opaque biock through which this slit is cut ismade sufficiently great so that the light which falls through this deepslit upon the convex mirror 3i is limited to a singlepicture elementorvline of the ground glass screen of the eamera upon which the scene to betransmitted is projected. Although the lightY thus picked up Vby thephotoelectricl cell from la singleY picture element is extremely small,it is possible by use of the now Well known-.electron multiplier tube toobtain adequate signal impulses With this form of direct pickup.Obviously, the intensity of the light isrenhanced byusing a very fastlens o VYshort focal length and locating the pickup mechassiVY nismclose to the small but brilliant picture which is projected upon theground glass screen of the viewing camera.V Y

In place of the 45 cenvex mirror 25, Yor 34, of

nthe attached figures I may employ a simple flat mirror and a doubleconcave, or'a plano-concave, lens suitably, located-in front of thisflat mirror, with the lens axis inline with the axis of the motorshaft.The action of Such lens will be to deflect the beam of light from the 45flat mirror,

and thereby-greatly accentuate the angle of deture of linea-r outline,a' second opaque member having a-linjear transparentn aperture, a lightsource, a system ofmirrors for reflecting the lightf from said sourcewhich projects through said apertures, and rneans for moving said partsso that the mirrors cause the light beam toi dene radial scanning paths.i

3. In a television system a stationary opaque member having a Zig-zaglinear transparent aperture therein, anopaque plate having a linear'transparentj aperture therein, a light source,

means for moving said plate and light source relatively toY saidstationary opaque memberg-and means for reflecting the beam froinsaidiight source to cause itto traverse radialpaths within a prescribedenvelope. Y

4. A television scanning system comprising a stationary opaquef: memberhaving a zig-zag linear transparent aperture therein, a source of light,an opaqueplate having alinear transparent aperture therein, means forprojecting a light beam through said transparent apertures to cause lamoving pencil of light to be projectedfgthrough said opaque member, andmeans for reflecting said pencil of light to cause it outline a radialYscanning pattern. 1;

5. A Ytelevisionk system comprising an opaque member having a Zig-zaglinear transparent aperture therein, an opaque plate having a' lineartransparent aperture therein, a source of light, a rst-,mirror arrangedat a 45 degree angle to g the direction of travel of said light beam, asecond 1 mirror arranged at a 45 degree angle in the Y directicn oftravel of said light beam after itis Y reflected fromsaid first mirror,and means for Y rotating said source or light, Yopaque plate and mirrorsabout said opaque member.

6. A television system comprising an opaque member having a zig-zaglinear transparent aperture therein, an opaque plate having a lineartransparent aperture therein, a source Eof light, a rst mirror arrangedat a 45 degree angle to the direction of travel of said light beamafterit is projected through said apertures, a second mirror arranged at a 45degree angle to the direction of light reflected from said rst mirror,means for rotating ,said source of light, opaque plate and mirrors aboutsaid opaque member,` and means for moving said opaque member to vary thescanning pattern. "Y

7. A television system comprisinggan opaque member having a zig-Zaglinear transp-arent aperture therein, an opaque plate having a lineartransparent aperture thereina source of light, a rst mirror arranged ata 45 degree angle to the direction of :travel of said light beam afteritis projected through sai-d apertures, a second mirror arranged at a 45degree angle to the direction of said light beam after it is reflectedfrom said :iirst mirror, means for rotating said source of light, opaqueplate and mirrors about said opaque memberyand means for modulating saidlight beam in accordance Withreceivedtelevision signals.

8.V A television system comprising an'opaque drum having a Zig-zaglinear transparent aperture therein, a light source, an opaque platehaving a linear aperture therein, means for rotating said light sourceand opaque plate about'said drum, a mirror at the center of said drum,andv means for rotating said mirror about the axis of said drum.

9'. A television system cemprising an opaque drum having a Zigi-Zaglinear transparent aperture therein, a light source, an opaque platehaving a linear aperture therein, means for rotating said light sourceand opaque platefabout said drum, a mirror at the center of said 'drum,means for rotating said mirror abeutthe axis of said drum, and means formodulating said light beam in accordance with received television sigin,said plate and member being arranged to pass-*75' a pencil of lightreiiected from said second mirror, a third mirror rotated by said motorshaft arranged at a 45 degree angle with respect to light reflected fromsaid second mirror and projected through said plate and member, and afourth mirror rotated by said motor shaft and arranged at a 45 degreeangle with respect to light projected from said third mirror.

11. A television system comprising an opaque member having a zig-zaglinear transparent aperture therein, an opaque plate having a lineartransparent aperture therein, an optical system for projecting a beam oflight through said apertures and reiiecting the same to dene a linearpath, a mirror, and means for periodically shifting said mirror to shiftsaid beam over a restricted area at right angles to its path.

LEE DE FOREST.

